Please refer to FIG. 1 showing a circuit diagram of a signal transceiver according to the prior art. The base of a transistor Q1 is electrically connected to an oscillator 12 which provides an oscillation frequency of 13.56 MHz. The base of the transistor Q1 is also electrically connected to a voltage divider 11 which is composed of resistors R1 and R2 for providing a voltage V1 to the base of the transistor Q1 to turn on the transistor Q1 at a correct working bias voltage. The collector of the transistor Q1 is electrically connected to an inductance-capacitance resonant circuit 13. When the transistor Q1 is turned on by the voltage divider 11, a carrier signal will be provided by the oscillator 12 to the transistor Q1 and transmitted out through the resonant circuit 13. When a transponder 14 receives the carrier signal transmitted from the resonant circuit 13, it will immediately return a data signal being modulated by means of amplitude-shift keying (ASK). Subsequently, the resonant circuit 13 of the signal transceiver receives the modulated wireless signal from the transponder 14, and the collector of the transistor Q1 generates a voltage variation. Since the voltage variation is weak and noisy, a rectifier 16 is used to rectify the voltage variation so as to eliminate the noise signal and generate a more stable and significant voltage variation. Finally, an envelope signal formed from the voltage variation is transmitted to an amplifier 17 to amplify the signal. Usually, a multi-stage amplification is executed to get better signals used for other circuit devices to determine the received data signals. In addition, a ferrite bead (FB) 15 connected between the resonant circuit 13 and the power supply is used to filter the noise signal.
As described above, for preventing distortion in signal transmitting process, quite a little hardware is set in the carrier signal transmitting and receiving circuits when designing a signal transceiver of an interrogator. Therefore, a lot of costs are consumed to overcome the distortion problem. Moreover, in the part of power system, a higher voltage, such as 9V, is used to provide a higher output power to enhance the signal. Therefore, how to reduce the supplying voltage for economizing energy is also an important subject.